Golf swing analyzing equipment

ABSTRACT

This invention is concerned with apparatus for diagnosing the characteristics of a golf swing, of the type in which one or more magnets attached to the golf club create signals in pick-up loops located near the ball position, or analysis to provide a readout of swing characteristics such as dynamic loft, dynamic lie (rake), impact position at the club-face, speed, and club face angle. Such apparatus is now improved by causing at least one loop or loop combination to be formed to provide at least two generally identical loop portions located side-by-side across the ideal swing path A-B with their respective adjacent edges parallel and closely spaced for defining therebetween a notional center line across the said path as an accurate sensed position. This is more accurate than sensing a single loop edge, and more sensitive. The respective loop portions, which can be formed from a single conductor or as two separate sub-loops, give balancing protection against the effect of extraneous electrical influence, and the increased accuracy and sensitivity can be used to decrease the overall extent of the loops in the travel direction. The club can possess magnets in the sole at the heel and toe, both inclined inwards at the top, to improve separation and decrease cross-talk. A method of club fitting in which the user selects optimum club characteristics for his established style of play is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

not applicable.

FIELD OF THE INVENTION

This invention relates to equipment for diagnosing departure from apreferred path or orientation, or other characteristics, of a objectoperated by a user in an attempt to follow that path correctly and in adesired orientation. In particular, it relates to an improvement in suchequipment as described in our copending application WO 92/22358 fordetecting, measuring and/or displaying differences for the desired idealperformance characteristics of a golf swing, and for convenience will bedescribed herein in that context.

BACKGROUND OF THE INVENTION

In that earlier invention a golf club is provided with at least onepermanent magnet typically held in a bore at a non-impact surface.Various configurations are possible, but a generally usefulconfiguration is to provide two magnets held in bores at the back of theclub, near the sole and equally spaced to either side of the centralplane of intended movement of the club head, i.e. as "heel" and "toe"magnets, with their axes "horizontal" and parallel to that plane.

This club is used in conjunction with one or more loops of electricallyconductive material, and in use in passed over a length of such loop togive an electrical signal. Using such a linear pickup gives bettersensitivity than the use of point magnetic sensors for the club headmetal, as known in earlier prior art. As each magnet crosses the linearpickup a characteristic "zero-cross" signal is produced, with a numberof measurable characteristics. The moment of cross-over relates to thezero value of this function. The symmetry of the zero-cross function isaffected by tilt of the magnets, i.e. tilt of the club face in one orother direction. The shape of the zero-cross function is related tominimum distance of magnet from pickup, as it crosses, being thus ameasure of height or (as difference of height between two magnets) ameasure of rake of the shaft.

Use of a number of inductive loops of different shape and placements inrelation to a designed ball position (such loops being for examplefabricated into a suitable mat) can thus give a multiplicity of signals,of varying shapes, symmetries and delays, from which a processing unitcan derive numerical values for angles (of loft, slice, hook or rake)speed, and displacements from an ideal path.

SUMMARY OF THE INVENTION

The equipment of the prior invention, and of the present invention, canbe used for two main and related purposes.

One is to provide, for a person desirous of improving his technique, adetailed analysis of all aspects of his club movement so that remedialaction can be taken. In this mode the equipment will find utility ingolf driving ranges, clubs, leisure centres, hotels and likeestablishments, being readily embodied in a coin-feed version if sodesired.

The other purpose is concerned with providing clubs for use byexperienced golfers. Each such golfer has individual characteristicswhich dictate the optimum choice of club, for example physical heightand reach, stance, speed of swing and general playing technique. Thisequipment can be used to quantify the dynamic elements of thesecharacteristics and thus to indicate clubs suited for that particulargolfer. In practice, it is envisaged to supply at point of sale a rangeof clubs and to select from that range, after a plurality of shots usinga known, magnetically-modified, club over the detecting loops of thepresent equipment, the optimum club to match personal characteristics.Equipment used for this latter purpose may be a simplified version ofthe fully diagnostic equipment, and can even be of a much simplifiednature usable only to test, e.g. speed, dynamic lie (rake) and/ordynamic loft. Alternatively, the standard diagnostic equipment can beprovided, but with some circuits switched off or disenabled.

Additionally to the above main uses, the equipment can itself be used ina game or competition mode, either for a complete set of holes, or e.g.in a driving or putting competition. The man skilled in the electronicart will have no difficulty in designing suitably modifying circuitry topermit such use.

The present invention sets out to provide an improved version of suchequipment in which the shape of the induction loops has been modified.As described below, embodiments can consequently be designed which havehigher timing accuracies and/or higher sensitivities, and/or innateresistance to extraneous electromagnetic fields; and which moreover canuse less power, so that a battery-driven embodiment will last longerbetween battery changes.

In one aspect the invention consists an apparatus for detecting,measuring and/or displaying differences from desired ideal performancecharacteristics of a golf swing, comprising: at least one golf clubhaving attached in relation to the club head at least one permanentmagnet at a predetermined location and orientation relative to the clubface; a detector array having a ball-position indication, and comprisingat least one sensor, for a magnetic field, located in a predeterminedsensing position relative to the desired ideal path of the club headover the ball position indication; and readout means electricallyconnected to the detector array to convert one or more electricalsignals produced by said sensor by swing of the golf club into a formsuitable for a detection signal, or for measurement or display,characterised in that the sensor is a plane loop, or loop combination,configured to provide at least two generally identical loop portionslocated side by side across the said ideal path with their respectiveadjacent edges parallel and closely spaced for defining therebetween anotional centre line across the path as a sensed position.

The loop portions are typically of a parallelogram shape. The end edgesof the parallelogram loop portions are preferably themselves aligned,and the parallelograms are preferably rectangles (including squareswithin that term).

The loop configuration as utilized in the present invention can beprovided in two main forms, namely a unitary form or a combined form.The unitary form provides the defined configuration from a single lengthof wire or the like conductor, shaped into the two parallelograms (e.g.rectangles) with a suitable electrical insulation expedient at anycross-over point, and with the respective free ends connected toprocessing and readout means for the signal. The combined form providesthe defined configuration from two identical side-by-side parallelograms(rectangles) each connected to the electrical circuitry for processingand readout, but via means permitting effective signal summation.

It will be appreciated that the configuration resembles to some extentthe figure "8" but with a transverse and doubled centre bar and aparallelogram e.g. rectangular format.

It will also be appreciated from studying the earlier application thatthe possibility is discussed therein of using two parallel plates with adefining sensed gap between them. The present invention however, asdiscussed in more detail below goes beyond such a concept to provide aloop configured to define spaced elements themselves defining a centralsensor line.

Our earlier application WO 92/22358 (GB 92/01105) moreover envisages toform the array from a plurality of loops at predetermined locations andorientation in relation to the ball indication position, the loops beingelectrically insulated from one another and collectively thereforepermitting a multiplicity of separate signals to be detected andanalysed or converted to a suitable form for measurement and/or displayfor each swing of the club. Preferably, such loops are of equalextension in the plane of magnet travel.

Generally, one or more of such loops, in accordance with the presentinvention, may be replaced by the configured `figure-of-eight` loop, asdefined above, with advantages as discussed below. It will beappreciated that although the notional centre line is a primary sensordatum, the other parallel loop edges can also be utilized for sensingand comparison purpose.

The number of magnets attached in relation to the club head can varyalthough, since their respective fields should not overlap to the extentthat confusion arises, a small number of magnets, specifically one ortwo magnets, is preferable. These can be fixed at the sole of the clubor at the back of the club. If only one magnet is used it willpreferably be located in a recess in the central plane of the club (inthe sole or at the back) i.e. that plane in which a hit ball willgenerally travel. If two magnets are used they can be spacedfore-and-aft in this plane, again in suitable recesses in the sole. Thisconfiguration is more suitable for wooden clubs. Alternatively, they canbe equispaced to either side of the central plane, in which case it ispreferred for the magnets to lie in such recesses at the back but nearthe sole. This configuration is more suitable for irons or a putter.

The magnets may be held in the recesses with their magnetic axes in thegeneral direction of ball travel path; or at right angles to this pathand generally "vertical" (in relation to a club held at rest on theground); or possibly even at right angles to the path and generally"horizontal" (again in relation to the grounded stationary club). Wheretwo magnets are used, and when these are spaced by a predeterminedamount e.g. equispaced to either side of the central plane (of desiredtravel) at the back or in the sole it is preferable to orient them inopposition i.e. with the N poles facing in opposite directions, to giveeasily distinguishable signals. If two magnets are spaced fore-and-aftin the sole, they can either be opposed or lie in the same direction.

One preferred range of such spacing is usually from 50 mm to 110 mm. Forexample, magnets in the sole of a wood, or back of an iron, aretypically spaced at 60 mm; at the back of a putter 100 mm is preferred.

Further arrangements of magnets may also be used, possibly depending tosome extent upon the primary purpose for which the equipment isinstalled, as discussed above.

Our prior application discloses the use of two magnets lyinghorizontally and spaced apart at the rear face of the club. Thiscombination can be used for all of the detection purposes indicated, butwe have now found that for a "wood" or "iron" (referring to historicstyles of club rather than necessary materials of construction) there isa valuable alternative placement of two magnets, separated to eitherside of the club-head median line and at the sole of the club, morepreferably at the heel and toe regions where the sole begins to trendupwards. In such a placement the magnets could be essentially "vertical"i.e. with their longitudinal axes orthogonal to the surface of theground at the bottom of the swing. Preferably, however, they are eachlocated at angles to the vertical in the plane at right angles to theswing. The angles of each to the vertical are typically the same ande.g. from 10° to 40° such as 20°. As described in more detail below,such an arrangement provides a sensitive and characteristic signal foreach magnet (especially when used with a ferromagnetic club), andmoreover slightly reduces "cross-talk" between the signals, i.e. theinfluence of the heel magnet in the toe region and vice versa. Suchmagnets can also be readily located at somewhat greater distances thanin the first two-magnet embodiment, e.g. at 75 mm or more, which furthersignificantly reduces "cross-talk".

Another magnet arrangement suitable for use (especially withcustom-selection equipment of a simplified nature) is that of a singlemagnet at the centre of the sole, whether horizontal, orthogonal toground, or tilted. Processing of the various signals from such a singlemagnet gives, in addition to speed of swing, information about dynamicloft (related to the actual orientation on impact of the face of adriver or like club in vigorous use at the end of its resilient shaft)which is a key feature in choice of such a club, even though as a singlemagnet embodiment it cannot give signals relevant to dynamic lie (shaftrake).

We have also discovered that there are several types of magnet mixingsuitable for use. While, for high-impact clubs some form of securingwithin an accurately dimensioned recess is usually preferable, it ispossible to allow some magnet projection, especially on faces remotefrom impact or otherwise advantageously located e.g. the upwardlyslanting heel and toe regions of the sole as discussed above. For aputter, (and especially for the protected environment of a store usingthe custom-selection equipment) it is possible merely to adhere themagnets, e.g. at marked positions. It is even possible that two magnetsmay be adhered (typically symmetrically and by their cylindrical bases)at the respective heel and toe regions of the front face of a putter,away from the impact zone, to give a club readily usable forcustom-choice of a putter, or for a simple "putting" game mode.

The magnets used are preferably the so-called "rare-earth-basedpermanent magnets", which can be fabricated in small sizes with highstrengths as measured by their "BH product". The NdFeB type of magnets,said to be approximately Nd₂ Fe₁₄ B, or the socalled "SECo₅ " magnets,as available under the Registered Trade Marks Vacodym and Vacomax fromVacuumschmelze GmbH of Hanau, Germany, when made up in cylindricalshape, 5-10 mm diameter and 3-10 mm length, e.g. 8 mm diameter and 5 mmlength, (the larger sizes are more suitable for putters) and axiallymagnetised with a BH product measured in KJ/m³ of 50-350, morepreferably 200-300, which magnets have a resistance to impactdemagnetisation, are valuable in the practice of this invention.

The loops themselves may be composed of wire, possibly wound in a numberof turns, or may be flat conductive ribbons of material or lines on aprinted circuit board. The actual width of the lines does not appear tobe critical.

Preferably the detector array is configured as a composite expansecomprising the loop as discussed above, with the two portionselectrically insulated one from another and from their surroundings, theupper surface of which expanse shows the ball position indication, andfurther comprising electrical connection means to connect the detecting,measuring or display device. The expanse can be a more or less rigid,impact-resistant plate if configured for woods or irons, but can be lessstrong e.g. a flexible mat if only putting characteristics are to bemeasured. It is valuable if an area of low-reluctance magnetic materialis located beneath the loops to enhance signal strength. The expansecould alternatively be of a periphery to allow placement around a ballin play e.g. on a putting green, to record and analyse the puttingswing.

The readout means of the apparatus for detection, measurement or displaycould be simply an intersection signal, to give an audible or visibleindication of fault. More preferably, it compries a digital or analoguereadout, of one or more parameters, obtained by computation based uponcombinations of signals received from different loops. Such computationmay be summarised on a display screen of a notional golf hole, showingwhere the ball would have travelled if hit with the recorded andanalysed swing.

The invention extends to the combination as defined either with a wholeset of clubs, or a selected sub-set of clubs e.g. one wood, one iron(such as a 5-iron) and optionally one putter, all suitably provided witha magnet or magnets. The magnets can be differently arranged dependingon the type of club.

Other aspects of the invention include a golf club head per se suitablyprovided with magnets as discussed above, and a mat comprising thedetector array of loops also as discussed above.

In particular this aspect envisages a golf club head, or golf clubcomprising such a head, suitable as a wood or iron and having twomagnets, located in recesses spaced to either side of the central planeof the head at the heel and toe regions of the sole portion of the club,with their magnetic axes lying generally in that plane perpendicular tothe line of travel of the club head and inclined inwardly e.g. at10°-40° at their upper ends. As indicated above, such tilt decreases the"cross-talk" between magnets. It is also easier to fabricate if the heeland toe regions of the bottom edge of the club are used for placement.

In a yet further aspect the invention consists in a method for userselection of an optimised golf club which comprises the steps: ofproviding for selection a range of golf clubs of different usercharacteristics; providing at least one diagnostic club of predeterminedcharacteristics, having located at the head thereof one or more suitablyoriented magnets as described above; providing diagnostic apparatus ofthe type described above; making available such equipment for a user toeffect a plurality of strokes of a like nature using the, or a chosen,diagnostic club; and thereafter selecting from the available sale range,and in the light of the recorded diagnosed results, a club to optimiseuser performance.

Selection of a particular club may be effected by consultation of alook-up table in the memory of the apparatus. For example, ashereinafter explained in greater detail, the diagnostic apparatus canindicate a certain "rake" position of the club head during a swing ofthe club. The rake indication can then be used to determine the specificface orientation of the selected particular club. Similarly, asmentioned previously, an indication of the actual orientation on impactof the face of the diagnostic club determines the dynamic loft of theselected club.

DESCRIPTION OF THE DRAWINGS

The invention will be further described with reference to theaccompanying drawings in which:

FIG. 1 shows a loop of electrically conductive material and the travelof a magnet over such a loop of a magnet, all as used in the prior art,

FIGS. 1a and 1b show typical zero-cross time-dependent waveformsgenerated by the loop of FIG. 1 and illustrate the certain systematicinaccuracies which may arise;

FIG. 2 shows one embodiment of a loop design in accordance with thepresent invention, and a travelling magnet;

FIG. 3 shows a time-dependent waveform of a signal generated by the loopof FIG. 2 and the magnets;

FIG. 4 shows another embodiment of loop design in accordance with thepresent invention, and a travelling magnet;

FIG. 5 shows time-dependent waveforms of a signal generated by the loopof FIG. 5;

FIG. 6 shows an arrangement of loops as illustrated in FIG. 2, which canbe arranged on a plate or mat, for use with a golf club carrying twomagnets; and

FIG. 7 shows another embodiment of loop design in accordance with thepresent invention.

FIG. 8 shows a particular alternative embodiment of magnet placement;

FIGS. 9a and 9b show diagrammatically other details of possible magnetplacement; and

FIG. 10 shows for each curve the signal given by one magnet in theplacement of FIG. 8, and in different swings, crossing a"figure-of-eight" loop, the magnets crossing at different heights andtilts above the notional ball position on the mat.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, a loop 11 of electrically conductive material has arectangular shape with a front edge 11a, a rear edge 11b and twoconnecting edges 11c, 11d. A magnet 12 passes over the loop, and gives asignal whenever it passes closest to one or other edge. As shown, edge11a is used to form this signal for pickup across connectors 17 andamplification at amplifier 16 for processing at 18.

As magnet 12 passes over the loop edge 11a e.g. along path A therespective poles induce a signal, first in one direction and then in theother, theoretically as shown in FIG. 1a, this being termed a zero-crosssignal. FIGS. 1a and 1b in each case show the instantaneous voltage V at18 (FIG. 1) against the instantaneous position X of the magnet 12. (Asimilar signal, of reversed polarity will be given at edge 11b). Thetime the magnet crosses the edge 11a is shown generally by thecross-over point P. If when crossing this line the magnet was higherthen the signal is less strong, as shown in FIG. 1b. However, across-over point R is still readily detectable. If and to the extentthat measurements are being made of signal amplitude as a measure ofdistance, the signal of FIG. 1b is less sensitive than that of FIG. 1a.

When these signals are measured to high timing accuracies, however,systematic error will arise. This is inherent in the nature of the loop11; essentially, to one side of edge 1a the field dies away to infinity,but to the other side it is affected by the necessary existence ofreturn loop edge 11b. The upshot is that the perceived electricalcrossover point P is advanced from the true mechanical crossover point.Moreover, the amount of such advance increases if the magnet travesesedge 11a at a greater distance (height), i.e. perceived R is advancedmore than perceived P. Thus, measurement of speed using two suchseparate detector loops, (which are typically traversed at differentheights) could be slightly inaccurate. Also, in a typical Preferredprior art embodiment two loops 1 are placed with their respective edges11a aligned and, perpendicular to either side of an ideal path, so thatwhere two magnets are used in a golf club, one traverses one loop andone the other. In such an instance differences in the two arrival timesare processed to indicate a misorientation of the club face, whiledifferences as between the function amplitudes can be an indication thatone magnet traverses its loop edge 11a at a different height from theother magnet over its loop edge, i.e. that the clubshaft is rakedimproperly. However, because the perceived crossovers P and R areadvanced by different amounts the processing unit "sees" such improperrake as affecting face orientation even though the club face mayactually be accurately aligned.

FIG. 2 shows in analogous form an embodiment of one proposed loopconfiguration for use in the equipment of the present invention.

This loop 21 has a front edge 21a, a rear edge 21b and two parallelclosely spaced straight intermediate edges 21c, 21d, the loop beingcompleted by top and bottom edges 21e, 21f, 21g and 21h, and thesequence being 21b-21e-21c-21f-21a-21g-21d-21h, between connectors 27leading to amplifier 26 and the processor unit V. Magnet 22 traversesthe loop 21 along path 25 from A to B.

The spacing between parallel portions 21c and 21d is small, and anotional centreline 24 runs down the centre of the narrow area thusdefined between 21c and 21d. The separation distance is typically a fewmillimeters, or as little as is consistent with accurately maintainedseparation, and is small compared with typical height of magnet travelover the centreline.

For convenience, such a loop will be referred to herein as a unitaryfigure-of-eight loop. In practice all such loops, whether unitaryfigure-of-eight, or combined figure-of-eight as discussed below have aclosely spaced parallel double edge configuration defining thecentreline.

FIG. 3 shows the complete signal when a magnet 22, crosses the wholeloop from A to B. This signal has peaks 28, 29, 30, 31, 32 and 33. Thereare also three crossover points 34, 35 and 36. The signal strength atpeaks 30 to 31 is approximately twice that which would be given by asimple zero-cross function with a signal loop edge. Thus:

(a) The perceived cross-over time at centre-line 24 is accurate becauseof the symmetrical unitary figure-of-eight loop structure, and staysaccurately the same over a range of magnet heights.

(b) The amplitude at effective crossover (at 24) is doubled, thusincreasing sensitivity and signal-to-noise ratio.

(c) The symmetrical nature of the unitary figure-of-eight loop balancesout extraneous interfering electrical signals such as those produced byother equipment in the vicinity using mains power In our prior artproposal special separate balance loops were provided for this purpose.

Also, advantage can be attained by arranging for the electricalcircuitry to lapse into a low-power-consuming stand-by mode betweenswings, and to be activated by a wake-up signal produced in dependenceon initial peak 28 as the club descends. This expedient increasesbattery life by decreasing power-consumption.

FIG. 4 shows analogously to FIG. 2 an embodiment of another loopconfiguration for use in equipment of the present invention.

Because of its shape and relationship to the configuration shown in FIG.2 this loop is referred to for convenience as a "combinedfigure-of-eight" loop. It is a combination of two mechanically separateloops the signals from which are combined and processed.

The two separate loops 50 and 60 have front edges 50a, 60a, rear edges50b, 60b, top edges 50c, 60c and bottom edges 50d, 60d. The respectiveloops are the same size and shape, and rear edge 50b of loop 50 andfront edge 60a of loop 60 are parallel and closely spaced, under thesame conditions as edges 21c, 21d of the unitary figure-of-eight loop ofFIG. 2, to define a notional centreline 70 (FIG. 4).

The loop are separately provided with electrical connection at 51 and61, each connection leading to amplifiers 52 and 62, of equal gain. Oneof the amplifier signals, from 62 as shown, is hen inverted at 63, andthe combined signal is taken off through equal resistors 54, 64 to givea combined signal for onward processing at 80.

The signal at 80 is generally similar to the signal produced from a"unitary figure-of-eight" loop as discussed above. It can be utilised inparticular to determine the exact moment of passage of the magnet 90across the notional centreline 70.

The man skilled in the art will appreciate that an additional amplifier,and additional summing components are required for the "combinedfigure-of-eight" loop in comparison with the requirement of the unitaryloop of FIG. 2, and moreover that this can lead to a slightly degradedsignal i.e. a signal of lower signal-to-noise ratio. However, thesedisadvantages are counteracted by the availability of different signals.

FIG. 5 shows the signals output at A, B and C, resulting from a magnet90 traversing on the dotted line, t₁, t₂ and t₃ being the perceivedcrossover points. The combination of two separate loops in a combinedfigure-of-eight loop gives three signals which in turn provide a methodof detecting height and tilt.

The signals thus generated can be processed as time events only. (Fromthese time events height and tilt data can be extracted). The unitaryfigure-of-eight loop, by contrast, requires both signal and amplitudetime event processing.

In FIG. 5 perceived t₂ is accurate for the mechanical crossover ofcentreline 70 (as in FIG. 2). The time difference between perceived t₃and perceived t₁, varies with speed and with the height of the magnetabove the loop plane. Any time inequality between perceived t₂ andperceived t₁, and between perceived t₃ and perceived t₂ is a measure oftilt of the magnet.

FIG. 6, shows a loop configuration of equipment according to theinvention, comprising a number of rectilinear "unitary figure-of-eight"loops formed by tracks on a double-sided through-hole-plated printedcircuit board 320, connected to amplifiers 341-348 and signal processingcircuits as shown.

Each circuit track forming a "unitary figure of eight" loop has at leastone section (typical examples are shown at 321 and 322) which cross overor under the main track and electrically connects to the main track bythrough-plated holes. For convenience, the printed circuit board 320 isdesignated with a right hand edge 323, a left hand edge 324, an arraycentreline 325 and a tee position 326. Two printed circuit tracks 331,332 on the downward-facing side of the printed circuit board each form a"unitary figure-or-eight" loop having lengthwise sections of tracksloping at nominally 45 degrees to the centreline 25. The slopingsections of tracks 331 and 332 are substantially straight and parallel.The ends of he "unitary figure-of-eight" loop formed by track 331 areconnected to the inputs of amplifier 341 and the "unitaryfigure-of-eight" loop formed by track 332 is connected to amplifier 342.Three printed circuit tracks 333, 334, 335 on the upward-facing side ofthe printed circuit board each form a "unitary figure-of-eight" loop,connected to amplifiers 343, 344 and 345 respectively.

The lines of symmetry of the three "unitary figures-of-eight" formed bytracks 333, 334 and 335 are co-linear and perpendicular to thecentreline. The "unitary figure-of-eight" formed by the track 334,encloses an area which is approximately symmetrical about the centreline325. The "unitary figure-of-eight" formed by tracks 333 and 335, isadjacent to track 334 and encloses areas above and below track 334.

A further three "unitary figure-of-eight" configurations are formed bytracks 336, 337 and 338 in a configuration similar to tracks 333, 334and 335 but displaced to the left. The ends of the "unitaryfigure-of-eight" loops formed by tracks 336, 337 and 338 are connectedto the inputs of amplifiers 346, 347 and 348.

The magnets 351, 352 are attached to the clubhead 350 typically beingembedded within the body of the clubhead 350. A toe magnet 351 ispositioned near the toe of the clubhead and a heel magnet 352 ispositioned near the heel of the clubhead. The magnetic axes of bothmagnets are substantially parallel to each other and to the sole of theclubhead, and are aligned along the normal direction of swing. The linejoining the centres of the magnets is substantially perpendicular to themagnetic axes, the centres being separated by a known distance. Thepolarity of the toe magnet is arbitrarily chosen with a South poleleading in the swing direction, and that of the heel magnet is reversedso that the North pole is leading.

During the execution of a golf swing, the heel and toe magnets pass overthe various "unitary figure-of-height" loops and corresponding signalsare generated and amplified in the eight amplifiers 341 and 348.

The heights of the "unitary figures-of-eight" formed by the tracks 334and 337 (measured along a perpendicular to the centreline 325) arechosen to be somewhat smaller than the separation distance between thetwo magnets. As a consequence, when the swingpath is nearly straight andcentred on the tee position, relatively little voltage is induced in theloops formed by the tracks 334 and 337, compared to the voltages inducedin all the other loops. However, when the swingpath is off-centre suchthat one or other magnet passes over the tracks 334 and 337, voltagesare induced in these loops with magnitudes equal to or greater than thevoltages induced in the off-centre loops. In this manner the swingpathcan deviate to some degree on either side of the array centreline 325,and signal content associated with the heel magnet can be discriminatedagainst signal content associated with the toe magnet. The amplifiedsignals from all eight channels are periodically sampled (typically at50 microsecond intervals) and the instantaneous value of the signal ineach channel is stored as a digital value (typically 8 bits pluspolarity). The sampled data representation for the sensor array signalsis then sorted and processed to decode and display various swingparameters.

When either magnet 351 and 352 passes over one or other unitaryfigure-of-eight loops, a signal in the form of that depicted in FIG. 2is generated in those loops. The processor examines the sequential datain all eight channels and executes the following initial computations:

a) The sequence and polarity of the major peaks emanating from thecentral unitary figure-of-eight loops 334 and 337 are examined toidentify these signals as being generated by either the toe magnet orthe heel magnet, and depending on this test, the signal from loop 334 isadded to that of loop 333 or loop 335, and similarly, the signal fromloop 337 is added to the signal of loop 336 or 338.

b) Having combined the signals as described in (a) the resultant sixremaining signals are examined and the magniture of the two major peaks(one positive, one negative) relative to the quiescent or zero signalvalues are determined.

c) The position of both major peaks in each of the six signals inrelation to an arbitrary time frame is determined and also the timeposition of the signal zero crossings between the peaks is determined.

From the above, all the data necessary to compute various components ofa clubhead's vector velocity and orientation are available.

The configuration for "unitary figure-of-eight" loops as depicted inFIG. 6 shows, For clarity, each unitary figure-of-eight" occupying aseparate part of the printed circuit board area. In practice, the"unitary figures-of-eight" may overlap in order to increase thecatchment area for the sensed magnetic fields. This entails, in general,an increase in the required number of cross-linking track sections(similar to section 321 and 322).

Alternative methods of fabricating the sensor array include the use ofconductive print techniques to create cross-linking sections or use of"stitched wire" construction where the required track patterns andconnections are formed from insulated wire.

A consequence of the loop combination used in the practice of thisinvention is that the overall loop dimension measured in the directionof travel of the magnet can be reduced, even compared to the single loopof our prior proposal. This is because when designing a single loop, asin this prior art, enough separation is required between the front andback edges to minimise the lag or lead of the electrical crossoversignal compared to the mechanical crossover point, and this requires alarge loop. In the present invention, the central doubled edges definethe key measurement line, and the proximity of the combined loop frontand back edges does not affect accuracy, so a smaller overall dimensioncan be achieved.

It follows from this that the two loops referred to in the descriptionand definition of the present invention, whether portions of a unitaryloop, or electrically separate part of a combined loop may themselves becart of a multiple, or higher-order, loop arrangement. In other words,the use of two loop portions can be fulfilled by the presence of threeor more such portions. The overall dimensions are still acceptablyconstrained.

FIG. 7 shows in a format generally equivalent to that of FIG. 4 a systemof three loops, electrically separate, combined into a combined loop.This loop defines accurate timing centrelines E and F, traversed bymagnet along path A-B and connected to a common output Va by amplifiers100, inverter 120, and resistors 130. The remaining features of FIG. 7can be established by reference to FIG. 4, and a combined signal withtwo accurately timed cross-overs, of the improved characteristicsdiscussed above, can be generated and processed.

FIG. 8 shows from the front the head 200 of an iron carrying in suitablerecesses a cylindrical toe magnet 202 and a like cylindrical heel magnet203, each in the embodiment shown being located to project slightly fromthe club head. The bottom of the club head, at the heel and toe regions204, 205 rises slightly whereby the projecting portions of the magnetsare, to some extent at least, safeguarded from contact with the mat (notshown).

The magnetic axes of the two magnets 202, 203 are inclined inwards asshown, while remaining in the general plane of the club head. It ispreferable but not essential to locate them both at the same angle x ofincline, e.g. 20°, but different angles could be used.

Because the extreme ends 204,205 of the club head are used to locate themagnets 202, 203 (whereby their spacing is maximal) and because themagnets are tilted as shown there is much reduced signal "cross-talk"between the two magnets as they cross the relevant signal-measurementlocation.

In practice the use of ferromagnetic "irons" or "woods" gives a higheramplitude signal than non-ferromagnetic materials in the embodimentshown in FIG. 8.

This embodiment as shown can be used (as described below) to give arange of signals useful for a fully diagnostic machine. It is howeveralso suitable for club-fitting or club-selection equipment of morelimited criteria and simpler construction. In such equipment, forexample, the use of "either" loops, to distinguish the signals from therespective magnets, might be dispensed with since "and" loons giveinformation relevant to dynamic loft i.e. the actual vertical impactangle with the ball which can only be ascertained for a given userdynamically, by actual strong use of the club, rather than statically.

While the loops in the mat can be modified, or selectively used, it isalso possible to modify magnet type and placement. For example, afurther simplification would be to attach the magnets externally, i.e.adhered and located as shown, but not recessed. This is a moremechanically fragile arrangement but may be adequate (and would beeasily repairable) in a store selling the optimal customised clubs basedon diagnosis of key criteria.

The simplification of magnet location number and placement can befurther pursued, for a less-demanding custom-fitting diagnosis of speedand dynamic loft, using a single sole-located central magnet 210, asshown in FIG. 9a. In practice, with suitable data processing a magnetwith magnetic axes horizontal, vertical or inclined could be used but ofcourse a vertically oriented cylindrical magnet is preferable since itcan be completely sunk into and adhered with a cylindrical bore, orsimply adhered by magnetic attraction to a suitable portion of the clubhead.

FIG. 9b shows another simplification, useful particularly for a putter,to give an indication of dynamic lie (shaft-rake). In this Figuremagnets 220, 221 are widely spaced with magnetic axes horizontal andwith end faces adhered to the extreme heel and toe regions 222, 223 of aputter face 224. This still gives an ample impact surface at 225. Theclub head can be readily constructed and repaired in a store (or home)environment, and is thus suitable for custom-fitting or competitive gamepurposes.

FIG. 10 shows two signal waveforms 230, 231 plotted on the sameamplitude scale and timebase scale. These waveforms have major peaks at232 and 233 and the quiescent or DC amplitude level for both signals isshown at 234. The waveforms of FIG. 10 also each have one major positivepeak 232, 233 and two lesser negative peaks 242, 243 and 252, 253. Thesepairs of peaks are analogous to the zero crossing points in FIG. 3,namely 35, 34 and 36 respectively. The peaks in FIG. 10 and the zerocrossings in FIG. 3 correspond to the points in time at which, in FIG.2, the magnet 22 (which is shown with magnetic axis horizontal, butwhich alternatively may be orthogonal to the plane of thefigure-of-eight) crosses the boundary 24 and its front and rear edges21a, 21b. Thus features in one waveform type, generated with magneticaxis orthogonal to the figure-of-eight plane, are analogous to featuresin the alternate waveform type, generated with magnetic axis horizontalto the figure-of-eight plane.

Features of particular interest in FIG. 10 are the time and amplitudeco-ordinates of the peaks 232, 233 (which are respectively analogous tothe time co-ordinate and the slew rate or slope of the zero crossingpoint 35 in FIG. 3), the slew rate or slope of the leading edges 235,236 and of the trailing edges 237, 238 of each major pulse (which areanalogous to the amplitudes of the leading and lagging peaks 30, 31 inFIG. 3) and lastly the time duration of each pulse, or pulse widths 239,240, measured at given amplitude co-ordinates which are some fixedproportion (e.g. half) of the respective peak amplitudes. The pulsewidths being analogous to the time separation between leading andlagging peaks 30, 31 in FIG. 3).

In FIG. 10, measurement of the peak amplitudes at 232 and 233 (relativeto the quiescent level 234) show these to be 5.90 major scale divisionsand 2.15 major divisions respectively, (within some measurementuncertainty). Similarly, the pulse widths 239 and 240 are found to be0.54 and 0.89 major scale divisions respectively. Relating thesewaveform measurements to the known heights of the magnet line of travel(32 millimeters and 53 millimeters as indicated in FIG. 10), it can beseen that the ratio of the peak amplitudes is inversely proportional tothe square of the ratio of the magnet heights, and that the ratio of thepulse widths is directly proportional to the ratio of the magnetheights. This leads to a method of measuring the magnet speed usingfeatures from only one signal derived from one loop circuit. Since themagnet height at a given speed of travel can be ascertained by therelative pulse shape only, the variation in pulse amplitude related toheight variation can be estimated and, assuming that the magnet strengthand measurement gain characteristics are known, the speed of magnettravel can be related to the pulse peak amplitude (corrected for heightvariation). This can also be implemented using analogous features in thesignal from of FIG. 3. In practice this would not be a preferred methodfor accurate speed measurement, as great consistency in magnet strengthsand amplifier gains is difficult to achieve.

Several of the present golf swing parameter measurements rely onaccurate detection of the instant at which a toe or heel magnet crossesabove a given sensor boundary. In FIG. 10 this instant is determined bythe exact time co-ordinate of a major peak, 232 or 233. In typicalimplementations of the invention, measurements of the waveform are takenat successive sampling intervals and subsequently processed as digitaldata. It is very improbable that an exact peak measurement will coincidewith any instant of measurement sampling. To obtain reliable andaccurate estimates of peak timings, the digital process uses a suitablemethod of numerical differentiation applied to several data samples ator near the waveform peak.

Whereas the planar arrays of loops described herein and in our priorapplication are considered to be practical and effective, it is realisedthat a wide range of alternate loop configurations and sensor typescould achieve similar elongate form and improved degree of magneticfield coupling. For example, the sensors could comprise various loops orcoils disposed vertically, horizontally or in a combination, andoccupying a volume below the playing surface. Magnetic field detectionmethods may also employ suitably shaped elements of low reluctancemagnetic material with either field coil sensing or other sensingdevices such as Hall-effect devices or magnetic-resistive devices. Anarrangement based on the above principles is described in our priorityapplication No. 9113188.8.

Other arrangements, based on the preferred planar loops configurationbut using two or more sensor planes to extract more detailed information(by measuring the field in three dimensions) can be implemented, ifcomplexity and cost are secondary.

I claim:
 1. An apparatus for detecting, measuring and/or displayingdifferences from desired ideal performance characteristics of a golfclub swing, comprising; at least one golf club including a club headhaving a club face, the golf club having attached in relation to theclub head at least one permanent magnet at a predetermined location andorientation relative to the club face; a detector array having aball-position indication, and comprising at least one sensor, for amagnetic field, located in a predetermined sensing position relative toa desired ideal path of the club head over the ball position indication;and readout means electrically connected to the detector array toconvert one or more electrical signals produced by the sensor by a swingof the golf club into a detection signal, comprising: the sensor being aplane loop means to provide at least two loop portions arranged in afigure eight configuration, one of said portions having a forwardelement and said other portion having a rear element, said loop portionelements being located side by side at a central portion of the figureeight configuration being disposed transversely to an ideal path; therear element being substantially parallel to and generally closelyspaced apart from the forward element as compared with a typical heightof magnet travel over said elements for defining therebetween a notionalcenter line disposed relative to a path defined by the golf club swingis sensed to enable the club head magnet to interact with said forwardand said rear loop elements to produce a swing indication signal havingthree teaks at one polarity and three peaks at an opposite polarity withthree zero cross over points so that the perceived cross over time at anotional center line is accurate due to the symmetrical unitaryfigure-eight configuration over a range of magnet pass over heightsrelative to said loop means.
 2. Apparatus as claimed in claim 1 in whichthe at least two loop portions are parallelogram loop portions. 3.Apparatus as claimed in claim 2 in which the parallelogram loop portionsare rectangular.
 4. Apparatus as claimed in claim 2 in which the loopconfiguration includes a single length of conductor material having freeends and shaped into the at least two loop portions with electricalinsulation at any crossover point and with the free ends connected tothe readout means.
 5. Apparatus as claimed in claim 3 in which the loopconfiguration includes two separate and identical side-by-side loopportions each having free ends connected to readout means for processingand readout, the apparatus including means to permit signal summation.6. Apparatus as claimed in any one preceding claim comprising aplurality of loops at predetermined locations and orientation inrelation to the ball indication position, each one of the plurality ofloops being electrically insulated from one another and collectivelytherefore permitting a multiplicity of separate signals to be detectedfor measurement and/or display characterized in that at least one of theplurality of loops is configured as a parallelogram loop portion. 7.Apparatus as claimed in claim 1 in which the golf club comprises asingle magnet.
 8. Apparatus as claimed in claim 7 in which the singlemagnet is located in a central plane of the golf club, the central planebeing the plane in which a hit ball will generally travel.
 9. Apparatusas claimed in claim 8, in which the single magnet is located in a soleportion of the golf club.
 10. Apparatus as claimed in claim 8 in whichthe single magnet is located at a back portion of the golf club. 11.Apparatus as claimed in claim 1 in which the golf club comprises twomagnets.
 12. Apparatus as claimed in claim 11 in which the two magnetsare located in a sole portion of the golf club.
 13. Apparatus as claimedin claim 12 in which the two magnets are located respectively at a toeportion and a heel portion, in the sole portion of the golf club. 14.Apparatus as claimed in claim 11 in which the two magnets are located ata back portion of the golf club.
 15. Apparatus as claimed in claim 11 inwhich the golf club is a putter, and in which the two magnets arelocated at the club face of the golf club.
 16. Apparatus as claimed inclaim 11 in which the respective magnets are attached to the golf clubin opposed magnetic senses.
 17. Apparatus as claimed in claim 11 inwhich the respective magnets are attached to a sole portion of the golfclub in the same magnetic sense.
 18. Apparatus as claimed in claim 11 inwhich the two magnets are located in a sole portion of the golf club,one of the magnets at a heel region and another one of the magnets at atoe region and each one of the magnets inclined, at an angle α of10°-40°, inwardly at respective upper ends of each of the magnets. 19.Apparatus as claimed in claim 1 in which the golf club is a putter andtwo magnets are attached, one to either side of an impact area, at theclub face of the golf club.
 20. Apparatus as claimed in claim 1 in whichthe golf club is a wood or iron with a single magnet recessed into asole portion of the club head.
 21. Apparatus as claimed in claim 11 inwhich each magnet is held in a recess in the club head.
 22. Apparatus asclaimed in claim 11 in which each magnet protrudes from the club head.23. Apparatus as claimed in claim 11 in which each magnet is adhered tothe club head.
 24. A diagnostic golf club comprising a club head for usewith a figure eight loop configuration having a sensed position definedby substantially parallel and substantially closely spaced apart centerelements of adjacent loop portions and suitable as a wood or iron, saidclosely spaced apart center elements being spaced by a short distance ascompared with the typical height of magnet travel over said elements,the club having two magnets, located in recesses spaced to either sideof the central plane of the head at about extreme ends thereof, beingthe plane in which a hit ball will generally travel, at the heel and toeregions of the sole portion of the club, with magnetic axes lyinggenerally in that plane perpendicular to the line of travel of the clubhead and inclined inwardly at 10°-40° at their upper ends, wherein thespacing between the magnets and the inclination thereof reduces signalcross-talk between the magnets as said magnets cross over the sensedposition to enable the club head magnets to interact with said centerelements to produce a swing indication signal having three peaks at onepolarity And three peaks at an opposite polarity with three zero crossover points so that the perceived cross over time at a notional centerline between the elements is accurate due to the symmetrical unitaryfigure-eight configuration over a range of magnet pass over heightsrelative to said loop configuration.
 25. A method for selecting anoptimized golf club for a user which comprises the steps of: providing aplurality of available golf clubs, each one of the plurality ofavailable golf clubs having a distinct user characteristic; using atleast one diagnostic golf club having a head of predeterminedcharacteristics, the diagnostic golf club having located at the headthereof at least one magnet at a predetermined location and orientationrelative to a club face of the head; using a diagnostic apparatusincluding a detector array, a sensor having a plane loop configured toprovide at least two substantially identical loop portions arranged in afigure eight, and readout means connected to the detector array toconvert one or more electrical signals produced by the sensor by a swingof the diagnostic golf club into a detection signal; executing at leastone swing by the user of the diagnostic club in cooperation with thediagnostic apparatus; determining a swing characteristic based ondetection signals corresponding to said at least one swing, saiddetection signal having three peaks at one polarity and three peaks atan opposite polarity with three zero cross over points; said determiningincluding determining the speed and height of the magnet relative to thesensor; determining from the speed and height and height and tiltcharacteristic of the swing of the user; displaying diagnosed resultscorresponding to said swing characteristic; and selecting a chosen clubfrom the plurality of golf clubs to optimize the performance of theuser, wherein said distinct user characteristic of said selected clubcorresponds to said swing characteristic.
 26. A method as claimed inclaim 25, further including using a look-up table to help select theoptimized golf club to optimize the performance of the user.